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Nico Rosberg 'positive' over Mercedes but admits pacesetters took fuel out on Day 4

Mercedes set fastest lap of the test on Saturday morning

By James Galloway at Bahrain

Last Updated: 23/02/14 9:48am

For the second successive session at the middle winter test the timesheet was headed by a works Mercedes driver, Rosberg setting a stunning 1:33.283 time on soft tyres - which a second quicker than team-mate Lewis Hamilton managed on the same compound on Day Three.

Rosberg's lap was also more than 1.6 seconds quicker than the next fastest Day Four runner, McLaren's Jenson Button, and within a second of his own pole time from last year's Bahrain GP despite the all-new 2014 generation cars not being expected to yet be anywhere near as quick relative to their predecessors.

And while Mercedes' latest show of strength undoubtedly appears ominous for the field, Rosberg suggested the Brackley team may nonetheless have been slightly flattered.

"In the morning I was doing some qualifying-style practices with lower fuel and that was good because I was feeling comfortable in the car," the German confirmed.

"I was able to push, we had a good balance and so I was pretty pleased with that. It's early days to say where we were because the other guys didn't take out as much fuel as we did, so we need to be very, very careful."

Nonetheless, there is a growing belief around the sport that Mercedes - many pundits' long-time tips for success in F1's new turbo era - have stolen a march on the field after the first two tests and are already clear favourites to win in Melbourne.

That feeling was strengthened by the sight of Rosberg completing a full 57-lap Bahrain GP race distance during the afternoon on Day Four and the driver himself admitted the team were in a "positive" situation with one test still to come.

However, Rosberg sounded a note of caution by pointing out that his two stoppages during the course of the day - which made it four for the week across his two days in the W05 - reminded the team that, like everyone else, they were not yet completely on top of reliability.

"For sure it's positive at the moment," he said. "In terms of reliability I managed to complete the race distance today, so that's been good.

"Nevertheless the car did break afterwards so there's still some way to go. So problems arising here and there, which is totally normal, and in comparison to other teams we are in a good position with reliability. But even us we need to be 100% bullet proof by the time we get to Melbourne, which is a massive challenge and very, very difficult. So that's where the focus needs to be on."

With quadruple World Champions Red Bull once more experiencing a difficult Bahrain test and trailing Mercedes by nearly 500 laps this winter, Rosberg added: "Definitely it's clear that we are ahead in testing at the moment with respect to reliability because they're struggling and we've done so many more laps than them and uncovered so many problems as a result which we're not able to resolve and cure."

The third and final pre-season test starts on Thursday morning in Bahrain. The Sky Sports F1 Online team will be providing live commentary from dawn until dusk on all four days, with live updates from trackside also on Sky Sports News.